The activity of single neurons in the lateral geniculate nucleus will be studied in behaving monkeys. Stimuli will be stabilized on the retina by surgical immobilization of one eye or by electronic stabilization of the retinal image. The maintained discharge rate and intensity response functions will be determined with diffuse light. Effects of sleep and wakefulness on the responses will be determined with particular reference to receptive field mechanisms. Properties and spectral sensitivity of a new receptive field component, the suppressive field, will be studied. Appropriate tests to distinguish between X and Y cells will be applied. Attempts will be made to identify interneurons of the LGN and specify their spectral properties. The effects of manipulating the reward value of the stimulus will be ascertained.